In the circuit below there is basically a resistance bridge with the inputs of an Op Amp connected across it. The output of the op amp is used to drive Q1 and would seem to create positive feed back via R5 and R2.
I suspect that this is designed to achieve constant current (or power?) through the bridge circuit but I am a bit confused as my limited knowledge of op amps suggests that the positive feed back will just cause the op amp to swing rail to rail and so just switch the transistor on or off.
Please can someone explain what Q1 is doing and how it would be affected by changing the bridge circuit resistor/thermistor values.
Thanks
I suspect that this is designed to achieve constant current (or power?) through the bridge circuit but I am a bit confused as my limited knowledge of op amps suggests that the positive feed back will just cause the op amp to swing rail to rail and so just switch the transistor on or off.
Please can someone explain what Q1 is doing and how it would be affected by changing the bridge circuit resistor/thermistor values.
Thanks